The present invention relates to a method and an apparatus for heat-sterilizing sealed containers filled with medical fluid by exposing the sealed containers moving along a slot formed through atop wall of an irradiator furnace to microwave irradiated from a square waveguide connected to the irradiator furnace into the latter.
It is commonly adopted to practice to sterilize the sealed container, e.g., the ampule filled with medical fluid particularly for infection during a process of manufacturing.
To realize such sterilizing treatment, various apparatuses utilizing microwave or auto clave have conventionally been employed.
Among them, the apparatuses utilizing microwave are disclosed, for example, in Japanese Patent Application Disclosure Gazettes No. 1973-59976 "Method and apparatus for sterilization of medical fluid contained in ampule", No. 1973-104381 "method and apparatus for ampule filled with medical fluid", and No. 1975-38985 "Apparatus for sterilization of ampule filled with medical fluid".
However, the methods and apparatuses of prior art utilizing microwave have been inevitable accompanied with a problem as follows. Specifically, an absorptivity for microwave generally depends on a conductivity of particular medial fluid and there are various ampules not only concerning their sizes but also concerning quantities of medical fluid with which these ampules are filled. Accordingly, if these ampules are irradiated with microwave under same conditions without proper consideration of such differences, the temperature rise ratio would be undesirably uneven depending on a particular kind of medical fluid and a particular size of the ampule.
None of the above-identified disclosures can accommodate different temperature rise ratio presented by different kind of medical fluid and, in consequence, these disclosures disadvantageously give rise to uneven sterilizing conditions.
According to the invention disclosed by the first mentioned Japanese Disclosure Gazette No. 1973-59976, a lower portion of each ampule standing upright is irradiated with microwave to minimize temperature difference within the ampule. However, a desired heating efficiency can not be achieved merely by irradiating the ampule with microwave unless a long heating furnace is additionally provided. Furthermore, this invention requires a relatively high microwave capacity and such requirement is another obstacle which makes an efficient sterilization impossible.
The invention disclosed by said Japanese Disclosure Gazette No. 1973-104381 can not achieve adequate sterilization for ahead of each sealed container since a temperature of medical fluid contained therein rises as said medical fluid absorbs microwave but a space confined within said heat does not absorb microwave and therefore no temperature rise occurs therein. Additionally, the temperature of said medical fluid which has once risen falls again upon contact with the container head. Thus, it is also impossible for this invention to achieve a satisfactory sterilization.
The invention disclosed by said Japanese Disclosure Gazette No. 1975-38985 requires a large-sized furnace as well as a considerably high microwave capacity and, depending on the kinds of medical fluid, it is difficult for this invention to obtain a sufficient temperature rise in the ampule. Moreover, the intensity of microwave is significantly uneven depending on locations within the furnace, so the individual ampules often present correspondingly different temperature rise ratios. In addition, adequate sterilization of the ampule head also can not be expected.
To compensate for such inadequate sterilizing effect of microwave, the prior art has employed the auto clave as auxiliary means. However, the auto clave makes it impossible to achieve a temperature control of the individual sealed containers and sometimes causes ingredients of medical fluid to be decomposed. Furthermore, the auto clave prevents the sterilizing treatment from being continuously done along a single process line.
To overcome such problems, the inventor of the present application has disclosed, in Japanese Patent Application Disclosure Gazette No. 1990-41162, a method for ampule sterilization utilizing microwave in which only a lower portion of each ampule is inserted through a slot formed through a top wall of an irradiator furnace connected to a square waveguide into the irradiator furnace so that a desired sterilization occurs doing movement of this ampule along the slot, said method being characterized by that a depth of the irradiator furnace or a distance between the ampule and a top surface of said slot is adjusted to control an irradiation amount for each ampule.
However, the invention disclosed in this Japanese Disclosure Gazette No. 1990-41162 relies only upon adjustment of the depth of the irradiator furnace or the distance between the ampule and the top surface of said slot inevitably resulting in a partiality of heating effect.